Tushar 1.6 - Cell division Flashcards
All phases of cell cycle
Interphase - G1, S, G2 - interphase is the metabolically active phase between cell divisions
Mitosis - PMAT
Cytokinesis
What happens during G1
- cell grows (rapid protein synthesis) + metabolic reactions
- proteins for DNA synthesis (next stage) are made
- mitochondria and chloroplasts (organelles) are duplicated
What happens during S phase
DNA is replicated - still is in the form of chromatin
What happens during G2
protein synthesis to make proteins needed for cell division
- chromosomes begin condensing
- preparation for cell division
- duplicate organelles
What is chromatin
- DNA is stored as chromatin during interphase
- it is loosely packed DNA
- it allows translation to happen for protein synthesis
What is chromosome
- DNA organises into chromosomes for mitosis
- tightly wound and condensed (via super-coiling)
- translation cant happen in this form
What are sister chromatids
These are genetically identical strands of DNA that are replicated (in S phase). They are held by centromeres.
What is mitosis needed for
- growth
- asexual reproduction
- tissue repair
- embryonic development
- cells also need to divide to maintain large SA:V, cells divide when they reach a certain size
What does mitosis do
Produces 2 genetically identical daughter nuclei
What happens in prophase
- SNA supercoils, chromatin –> chromosomes
- nuclear membrane breaks down
- spindle fibres completely form by the end of prophase
- centrosomes move to opposite poles
What happens during metaphase
- spindle fibres (microtubules) from centrosomes attach to the centromeres (kinetochores) of each chromosome
- microtubule depolymerisation = spindle fibres contract and shorten, this aligns the sister chromatids along the centre of the cell (equatorial plate/metaphase plate)
What happens during anaphase
- spindle fibres continue to shorten, causes sister chromatids to separate, now they are referred as chromosomes
- chromosomes pulled to opposite poles
What happens during telophase
- spindle fibres dissolve
- nuclear membrane + nucleolus formed
- chromosomes uncoil to chromatin
- beginning of cytokinesis
Mitotic index
Number of cells in mitosis/total number of cells
Used to predict how quick cancer could spread + response of cancer cells to chemotherapy
Cytokinesis in animal cells
Cytokinesis is the division of cytoplasm
1) Microfilaments (contractile protein) located beneath the cell membrane at the equator pulls the membrane inward
2) this forms a cleavage furrow
3) when cleavage furrow reaches centre, the cell in pinched apart into 2 daughter cells
Cytokinesis in plant cells
1) carb rich vesicle form golgi apparatus form a row at the centre of the cell
2) The vesicles fuse, forming an early cell plate
3) Cell plate grows outwards (by more and more vesicles being brought in), and then the cell plate fuses with the cell wall, dividing into 2 daughter cells
What are cyclins and how do they work
- cyclins control the progression of the cell cycle
- they bind to enzymes called cyclin-dependent kinases (CDKs)
- when cyclin binds to CDK, activated CDK attaches phosphate group to a target protein in the cell (this is phosphorylation)
- this makes the protein active, the protein will carry out tasks specific to the phase in cell cycle
- after even is done, the cyclin is degraded
- cyclin levels peak when their target protein is required
Different types of cyclins
Cyclin B: triggers move from G0 to G1 and G1 to S
Cyclin E: prepares cell from DNA replication in next phase
Cyclin A: activates DNA replication in S phase
Cyclin B: promotes assembly of mitotic spindle + preparation for mitosis
what is tumor and different types
tumor: abnormal cell growth resulting from uncontrolled cell division
benign tumor: tumor that does not spread to other parts of the body
malignant tumor: tumors that can spread to other parts of the body (cancer)
What are mutagens
Agents that cause mutations Mutagens can be: - physical: radiation - biological: viruses - chemical: e.g. arsenic
most mutagens are carcinogens (mutagens that lead to cancer)
Oncogenes
are mutated genes that contribute to the development of a tumor
- proto-oncogene: stimulate cell cycle + growth, cancer occurs when proto-oncogenes are mutated
- tumor suppressor gene: gene that goes against cell cycle and causes cell death (prevents cancer)
What is metastasis
- movement of cells from a primary tumor to other parts of the body where they develop into secondary tumors
- secondary tumors are made of same types of cells as primary tumors
1) cancer cells detach from primary tumor
2) they can the ability to penetrate walls of vessels to circulate around the body
3) circulated cells invade different tissues and develop into secondary tumors by mitosis
Smoking and cancer
strong positive correlation between frequency of smoking and development of cancer
cigarette smoke has many carcinogens
